Getting the lung to remember flu

After influenza infection, some memory T cells enter the lung and become resident memory T cells (TRM). Although TRM play an important role in conferring protection against subsequent flu infections, TRM in the lung do not persist. Understanding how to improve TRM persistence is a longstanding goal in flu vaccination. Using a mouse model of flu, Slütter et al. report that TRM in the lung are prone to die and need to be constantly replenished from the circulating pool of memory T cells. Because circulating memory T cells wane with time, the lung eventually runs out of TRM. Given that immune cell infiltration can interfere with breathing, the lung may have evolved to limit immune cell residence.